Phototube



H. STEYSKAL Sept. 3, 1940.

PHDTOTUBE Filed July 26, 1938 INVEN TOR. ERBERT S 7' E YSKAL Patented Sept. 3, 1940 UNITED STATES PHOTOTUBE Herbert Steyskal, Berlin, Germany, assignor to General Electric Company, a corporation of New York Application July 26, 1938, Serial No. 221,290 In Germany September 27, 1937 8 Claims.

My invention relates to electron discharge devices and more particularly to phototubes in which secondary emission amplification is produced.

Phototubes are known in which the photoelectric current may be amplified by an additional electrode arranged to release secondary electrons when bombarded by electrons emitted by one of the other electrodes. In these tubes the photocathode and secondary electron emitting cathode or electrode are usually situated opposite each other, while an anode having substantially the shape of a rod is situated midway between the photocathode and the secondary electrode. The photocathode is illuminated either through a window in the secondary electron emitting electrode or where the photocathode is of the transparent type the illumination is transmitted through the photocathode from the rear. This electrode .arrangement has the disadvantage that the anode which has the highest positive potential, is situated between the two electron emittin electrodes. In view of the fact that the anode is situated in the path of the electrons moving from the photocathode to the secondary electron emitting electrode, not all of the electrons released at the photocathode can reach the secondary electrode and a certain part of the primary electrons pass directly to the anode without producing an amplification through release of secondary electrons.

In accordance with my invention an electrode is employed in a phototube having a secondary electron emitting electrode which not only produces a shielding effect but also an amplification through a further emission of secondary electrons This shielding electrode placed in the electron path between the cathode and the secondary electron emitting electrode may form a fiat or preferably curved arcuate surface which partially surrounds or encloses the anode.

The principal object of my invention is to provide an improved type of secondary emission amplification phototube in which the primary photoemission is more efficiently utilized in producing an amplified current output.

The novel features which I believe to be characteristic of my invention are set forth with particularly in the appended claims but the inven-- tion itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which:

Figure 1- is a perspective view with the envelope partially broken away of a phototube made in accordance with my invention;

(Cl. 250-166) I Figure 2 is a transverse sectiontaken along the lines 22 in Fig. 1; and

Figures .3 and 4.- are similar transverse sections of two modifications of phototubes made in accordance with my invention. 5

One embodiment of a phototube made in accordance with my invention, as shown in Figure 1 comprises an envelope I0 provided with the usual base II and stem I2. Supported from the stem I2 is a conventional semi-cylindrical arcuate shaped photocathode I3 which may be coated on its inner or concave surface with any conventional light sensitive coating such as caesium or other alkali metal. Opposite the cathode I3 and preferably concentric therewith, there is provided a secondary electron emitting electrode which, in the modification shown, is in two arcuate shaped segments I4I4a, the inner or concave surface of which is likewise preferably coated with alkali metal for the purpose of increasing its secondary electron emitting properties. Between the photocathode I3 and secondary electron emitting electrode I l-44a. and preferably at their common center of curvature is an electron collecting anode I5 which, asshown in the drawing, may be a rod or a conductor extending along the longitudinal axis of the tube.

In accordance with one teaching of my inven-' tion, I dispose'between the photocathode I3 and the anode I5 a semi-cylindrical or arcuate shaped shield electrode IS, the outer or convex surface of which is similarly coated with a, material having high secondary electron emitting. properties. The convex surface of the shield electrode I6, however, may be smooth or shiny, such a surface also providing a good secondary emitting surface. As shown in the drawing, the shield electrode I6 is imperforate to prevent electrons from'the cathode I3 flowing directly to the anode I5. Positive potentials are applied to 40 the electrode I I-I la, the shield I6 and the anode I5 such as by the batteries I'I, I8 and I9 so that these electrodes are progressively more positive with respect to the photocathode in the order named. 4

As a result of the shape of, and the field distribution between the electrodes, the photoelectrons liberated from the photocathode I3 under the influence of light projected thereon through the envelope and between the secondary emitting electrode I4I4a,, are focused and directed upon the convex surface of the shield electrode I6 whereupon secondary electrons are liberated from the convex surface and directed upon the secondary cathode I4I4a by reason of the dife secondary electron emission from the concave surface of the secondary cathode I ll la.

While I have shown in connection with the above illustrative example one 'mjodificationof a phototube incorporating my invention," it may be desirable for certain applications to provide the photocathode l3 and secondary: electrode :14 directly on the wall of the envelope -l'fl,-s'uch' as shown in Figure 3. In this modification, I prefer to make the photocathode l3 of the semi-trans parent type sothatlight may be directed upon the photocathode from:its convex side. modification of my-invention, it isunnecessary to form the secondary electron emitting electrode [4 in segmented sectionslso that it likewise may be deposited directly, preferably as a metallic film, on the inner wall of the envelope l opposite the photocathode 13, the anode l and shield cathode l6 occupying corresponding positions as shown in Figure 1..

A further modification of my invention is shown in Figure 4 in which the photocathode i3 lies in a. single-plane, the secondary electron emitting electrode I4-l4a being segmented and oppositely disposed therefrom. Intermediate the photocathode I3 and the section M of the secondary cathode, I provide an anode l5 and shield cathode l6 similar to the form shown in Figure 1 and likewise between the section Ma and the cathode. l3 another :anode I50. and associated shield cathode l6a; In'this modification the two sections l4l4a of the secondary cathode are connectedtogetheras-are the anodes l5-l5a and shield cathodes: |6--l6a,:l these electrodes being similarly'connectedto sources of potential as shown in Figure-Lug.

. While I have indicated-the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application-for which. myv invention may be employed,

it'willbe. apparentlthat my invention is by no means limited tothe.exactformsillustrated or to the use indicated but that'many variations may be madeinthe particular structure used and the purpose for which it is employed without departingfrom the scope of my invention as set forth in the "appended .claims.

I claim:

1. A phototube including an envelope enclosing an arcuate shaped photocathode, a secondary electron emittingr electrode having arcuate shaped segments oppositelydisposed'from said photocathode, an electron collecting anode symmetrically positioned with respect to said photocathode and said secondary emitting electrode and a secondary electron emitting shield between said anode and said photocathode partially enclosing said anode. l

2. A phototube enclosing within an envelope a photocathode, an oppositely disposed multiply segmented secondary electron emitting electrode, an anode between each of the segments of said electrode and said photocathode and a secondary electron emitting shield between each anode and said photocathode 3. A phototube including an envelope containing a photocathode in the form of a plate of extended area, an output anode, an imperforate secondary electron emitting electrode having an extendedarea less than that of said photocathode positioned between said anode andsaid photocathode to prevent photoelectrons'moving directly from said photocathode to said anode, and another secondary electron emitting electrode facing said photocathode and wholly exposed to the side of said anode opposite said photocathode.

4. A phototube including an envelope containing a photocathode, an output anode, an arcuate secondary electron emitting shield electrode partially surrounding said output anode and having .its' convex surface facing said photocathode and I having an opening on the side thereof away from said photocathode, said adcuate shield electrode being between said photocathode and said anode, and another secondary electron emitting electrode exposed to said anode through theopening in said arcuate secondary emitting shield. electrode, oppositely disposed from said photocathode and lying wholly beyond said arcuate secondary emitting electrode with respect to said photocathode.

5. A phototube including an envelope enclosing a photocathode, a secondary electron emitting electrode having an arcuate segment with its concave surface facing, and oppositely disposed from, said photocathode, an electron collecting anode symmetrically positioned with respect to said photocathode and said secondary emitting electrode, and a secondary electron emitting shield electrode between said anode and said photocathode partially enclosing said anode.

6. A phototube including an envelopecontaining an arcuate photocathode, an output anode substantially at the center of curvature-of said arcuate photocathode, an arcuate secondary electron emitting electrode partially surrounding said anode having its convex surface facing the concave surface of said photocathode, and another secondary emiting electrode oppositely disposed from said photocathode and said arcuate secondary emitting electrode with respect to said anode and exposed to said anode.

7. A phototube enclosing within an evacuated envelope an arcuate photocathode, an arcuate secondary electron emitting shield electrode having the same center of curvature as and a smaller radius of curvature than that of said photocathode positioned with its convex surface facing the concave surface of said photocathode, an output anode at the center of curvature of said shield electrode and a secondary emitting electrode oppositely disposed from said photocathode and tocathode and said anode, and a secondary 'elec-' tron emitting electrode facing said photocathode and wholly exposed to said anode.

" HERBERT STEYSKAL. 

